Existing models of the relationship between attitudes and sexual risk taking behavior assume that sexual behavior is primarily the result of rational decision-making. However, sexual behavior is only partly "rational" in that risk-taking can be a result of automatic or unconscious processing, physiological states (e.g., sexual arousal), and substance use and abuse. In addition, risk-taking is associated with individual differences, particularly impulsivity and sensation-seeking. The primary goal of this proposed research is to better understand the sexual decision-making process that leads to HIV risk behaviors. By reaching a better understanding of these processes, we will better be able to both design and target effective interventions to reduce sexual risk-taking behavior in the context of substance use and abuse and with it the risks of HIV, other STDs and unwanted pregnancy for adolescents and young adults. We will also test and refine a dual-process model of sexual decision-making that focuses on the circumstances under which the decision-making process is more automatic as opposed to logical/rational and within conscious awareness. The specific aims of the proposed project are to: further develop and refine a methodology for assessing the impact of individual difference variables, sexual arousal, and substance use on sexual decision-making and HIV risk behaviors in substance using young adults; assess the impact of impulsivity and sensation-seeking on sexual decision-making and HIV risk behaviors in substance using young adults; assess the impact of perceived partner risk on sexual decision-making and HIV risk behaviors in young adults; assess the impact of sexual arousal on sexual decision-making and HIV risk behaviors in substance using young adults; assess the impact of marijuana use on sexual decision-making and HIV risk behaviors in young adults; better understand the process and outcomes of sexual decision-making for gay men; and assess the impact of gender and race on sexual decision-making and HIV risk behaviors in substance using young adults. We propose in-depth interviews, reaction groups and a series of six experimental studies. As a result of these studies, we will determine the impact of impulsivity, sensation-seeking, sexual arousal, and substance use on the sexual decision-making process and consequent HIV risk behaviors.